In geothermal power generation, hot water collected from a production well (hereinafter referred to as geothermal water) is used to produce power. The geothermal water having been used to produce power is reinjected into the ground again.
Geothermal water contains greater amounts of calcium ion, dissolved silica, and the like than does well water and river water and hence tends to cause deposition of scale, such as calcium carbonate and amorphous silica. As a result, scale is deposited along a channel in a geothermal power plant and a well through which geothermal water having used to produce power is reinjected (hereinafter referred to as reinjection well), and the deposited scale narrows or otherwise blocks the channel, possibly resulting in an insufficient amount of reinjected hot water. If a sufficient amount of reinjected hot water is not provided, a reinjection well needs to be newly dredged, resulting in an increase in cost. Since the dredging cost risks the power generation business, the business risk increases if the degree of blockage of a reinjection well (blockage speed) cannot be estimated in advance.
In view of the fact described above, attempts to pre-evaluate the state of scale deposition have been made, as described in Non-patent Documents 1 and 2.
Non-patent Document 1 discloses that hot water is supplied to a filled layer made of a porous medium and the difference in pressure between the inlet and the outlet of the filled layer is determined to observe phenomena such as the change in coefficient of permeability of the filled layer due to scale deposition and the distribution of the amount of scale deposition along the distance.
Non-patent Document 2 discloses that hot water is allowed to flow through pipes having different diameters and the state of scale deposition is observed in each of the pipes.